The present invention relates to apparatus for manipulating sheets which consist of paper or the like, and more particularly to improvements in apparatus for manipulating sheets which are transported in the form of a so-called scalloped stream wherein the leader of each next-following sheet overlies the trailing end or portion of the respective preceding sheet. Still more particularly, the invention relates to improvements in apparatus for counting successive sheets of a stream of partially overlapping sheets, especially for the purpose of accumulating the sheets into stacks containing predetermined numbers of overlapping sheets.
It is already known to utilize a monitoring device which is placed next to the path of sheets in a stream of partially overlapping sheets and is designed to generate signals in response to advancement of the leaders of successive sheets therealong. As a rule, the monitoring device is placed close to the center of the path of the stream, i.e., midway between the lateral marginal portions of the sheets which constitute the stream. In many instances, the monitoring device comprises a sensor which is mounted on a carriage. The latter is pivotable or otherwise movable while tracking the leaders of successive sheets in the stream. The sensor is operatively connected with a counter which transmits signals in response to advancement of predetermined numbers of sheets past the sensor; such signals can be used to indicate the detection of a preselected number of sheets and/or to regulate the operation of devices downstream of the monitoring station.
A drawback of the just described conventional apparatus is that the sensor is likely to skip certain sheets, especially when the speed at which the sheets are transported past the monitoring station is increased above a threshold value which, at the present time, is in the range of approximately 14,000 sheets per hour. In other words, if the counter generates signals which are transmitted to a sheet stacking or gathering device, successive stacks of superimposed sheets are likely to contain different numbers of sheets if the speed of advancement of sheets exceeds the threshold value.